1. Field of the Invention
The present invention relates to a technical field of a magnetic tape cassette and an injection molding method in case of molding a resin product for the magnetic tape cassette with molding dies, and more particularly, relates to a cassette half for forming a case of the magnetic tape cassette for accommodating a magnetic tape wound around a pair of take-up hubs and a molding method for molding the cassette half, a magnetic tape cassette provided with an improved friction sheet for preventing static charge of the magnetic tape and keeping slidability of the magnetic tape, and a magnetic tape cassette improved in detachability to a cassette automatic delivery apparatus.
2. Description of the Related Art
For example, a magnetic tape cassette used to an audio system or a computer may be exemplified as one example of the resin product. In general, the magnetic tape cassette has a structure in which a pair of hubs around which the magnetic tape is wound are rotatably incorporated and retained in a case body formed of upper and lower cassette halves coupled together in a lid-alignment manner. Such cassette halves are injection molded of thermoplastic resin such as PS (polystyrene), or ABS (acrylonitrile butadiene styrene resin) general. In order to observe and confirm the winding condition of the magnetic tape from the outside, the cassette halves as a whole are made of transparent material such as AS (acrylonitrile styrene) or PS, or a window portion that is transparent or semitransparent is formed in the opaque cassette half bodies.
Conventionally, this window portion is formed by adhesion with adhesive or supersonic welding of the window material molded separately from the cassette half bodies. However, in this case, since the molding step and adhesion step for the window portion are required, there is a restriction on a design and productivity is not so good. Accordingly, recently, the cassette half bodies and window portions are integrally molded through a color injection molding (or multi-color injection molding) method.
FIG. 8 is a plan view of an upper half of a conventional magnetic tape cassette.
A window portion 112 that is transparent or semitransparent is provided in the upper half 110 for observing and confirming the winding condition of the magnetic tape accommodated in the cassette halves from the outside. A pair of ribs 114 and 116 are provided for positioning and regulating the take-up hubs around which the magnetic tape is wound in this window portion 112. These ribs 114 and 116 are divided into two portions, for example, 114a and 114b, and arranged in the circumferential direction in conformity with the shape of the take-up hubs.
A cross-sectional view taken along the line IXxe2x80x94IX of FIG. 8 is shown in FIG. 9.
As shown in FIG. 9, position regulating ribs 114 (114a, 114b) of the take-up hubs are formed in the window portion 112 of the upper half 110 with a height in such an appropriate range that they can regulate the position of the take-up hubs and do not prevent the rotation of the take-up hubs.
A state that the window portion 112 is molded by means of, for example, the two-color injection molding method is shown in FIG. 10.
Molten resin is injected into a space (cavity) surrounded by a front mold (cavity side part) 120a and a movable half (force side part) 120b of the molding dies and a slide core 122 to form the upper half body 110. Thereafter, as shown in FIG. 10, the slide core 122 is slid by a thickness of the window portion 112. Transparent or semitransparent resin is injected from a gate 126 into the space (cavity) 124 formed therein to form the window portion 112.
At this time, recesses 128 (128a, 128b) for take-up hub position regulating ribs 114 (114a, 114b) to be formed in the window portion 112 are formed in the slide core 122.
However, in the case where the window portion 112 of the upper half of the magnetic tape cassette is formed by the injection molding as shown in FIGS. 8 and 9 like the above-described conventional case, there are the following defects. Namely, as shown in FIG. 10, the molten resin injected into the cavity 124 from the gate 126 flows as indicated by the arrows. In the flat portion, the resin flows horizontally without any deflection but in the recesses 128a, 128b corresponding to the portions of the take-up hub position regulating ribs 114 (see FIG. 8), the resin enters the inside thereof once, and thereafter, again returns to move further forward. Also, at this time, the recesses 128 (128a, 128b) are directed in a direction perpendicular to the advance direction of the resin and the flow is further obstructed. Furthermore, if a gas that is generated due to heat is contained in the resin, the flow of the resin is further obstructed.
Thus, since the molten resin is filled to ride the portion of the take-up hub position regulating ribs 114 (see FIG. 8), the fludized layer of the resin is advanced while being subject to the resistance. As a result, the resin is spread and advanced more in the portion where no take-up hub position regulating ribs 114 are provided. As shown in a plan view of FIG. 11, the flows of the resin coming in the two directions are brought into contact with each other at the end portion of the window portion 112 (the final filling portion of the resin). As a result, an abnormal color portion having streaks that are called welds 130 is formed at the joint portion to cause a problem in that the outer appearance becomes worse. In particular, since the window portion 112 is transparent, there is a problem in that such a quality reduction is undesirable.
By the way, as well known, in the magnetic tape cassette, under the condition that the respective end portions of the longitudinal magnetic tape are fixed to the pair of take-up hubs, respectively, the pair of take-up hubs around which the magnetic tape is wound are accommodated in a cassette bodies (upper half and lower half). Only a part of the magnetic tape tensioned between the pair of take-up hubs is exposed to the outside of the cassette body such that the magnetic tape may be brought into contact with a magnetic head at least when the cassette is loaded on a recording/reproducing apparatus of the magnetic tape.
When the magnetic tape cassette is loaded on the recording/reproducing apparatus, the part of the magnetic tape tensioned between the take-up hubs and exposed from the cassette body is brought into contact with the magnetic head within the recording/reproducing apparatus, the take-up hubs are rotated, the magnetic tape travels and slidingly contacts with the magnetic head within the recording/reproducing apparatus, and the magnetic head records information onto the magnetic tape and reproduces the information from the magnetic tape.
In an audio magnetic tape cassette, when the magnetic tape cassette is loaded on the recording/reproducing apparatus, the part of the magnetic tape tensioned between the take-up hubs and exposed from the cassette body is brought into contact with the magnetic head within the recording/reproducing apparatus, the take-up hubs are rotated, the magnetic tape travels and slidingly contacts with the magnetic head within the recording/reproducing apparatus, and the magnetic head records information onto the magnetic tape and reproduces the information from the magnetic tape. In a cassette having a front cover for protecting the tape such as a video magnetic tape cassette, when the magnetic tape cassette is loaded on the recording/reproducing apparatus, the front cover is rotated and moved to a position where the magnetic tape is opened by a mechanism within the recording/reproducing apparatus in cooperation with the loading operation. The part of the magnetic tape tensioned between the take-up hubs is thus exposed from the cassette body. Then, the take-up hubs are rotated, and the magnetic tape travels and slides in contact with the magnetic head within the recording/reproducing apparatus, so that the magnetic head records the information onto the magnetic tape and reproduces the information from the magnetic tape.
When the magnetic tape moves up and down or meanders upon the travel thereof, the magnetic tape is not exactly contacted with the magnetic head or slid well. Thus, the appropriate recording/reproducing is impossible. Also, there is a fear of a cause of other breakdown. Accordingly, it is necessary to suppress the up-and-down movement or meanders upon the travel of the magnetic tape, to enhance the regulating precision of the travel position of the magnetic tape and to stable the traveling property.
For this reason, conventionally, in the magnetic tape cassette using flangeless type take-up hubs, a pair of friction sheets are interposed between the take-up hubs around which the magnetic tape is wound and the cassette bodies (upper and lower halves) to thereby regulate the travel position (height) of the magnetic tape to adjust the travel position of the magnetic tape. Furthermore, a linear stamped portion (drawn portion) is provided on the friction sheet to regulate the travel position (height) of the magnetic tape by the height of the drawn portion.
On the other hand, when the thickness of the magnetic tape is equal to or less than 10 xcexcm, depending upon the magnetic surface and the kind of the base material, the tape edge of the magnetic tape becomes sharp so that the durability of the material that contacts with the tape edge, such as the friction sheet causes a problem. Further, the surface electric resistance value of the magnetic surface of the magnetic tape and the base material is in the range of 1xc3x97105 xcexa9 to 1xc3x971012 xcexa9. There is a problem of the fear of breakdown such as sticking of the magnetic tape to the mechanism elements or an adverse affect to the recording/reproducing apparatus due to the electric charge caused by the friction when the tape is entrained at a high speed. In particular, the longer the length of the magnetic tape, the larger the effect thereof will become. Therefore, there is a problem in that the tape is likely to be electrically charged.
By the way, this friction sheet (hereinafter simply referred to as a sheet) is formed in general of high-density polyethylene resin (high density PE) or the like, and the electric resistance value thereof is very high at about 1016 xcexa9. For this reason, the sheet itself is likely to be charged. The sheet is readily charged and stuck with dust by the contact or the sliding contact of the sheet with the cassette inner wall surface, the magnetic tape or the take-up hubs. The magnetic tape or the take-up hubs are brought into sliding contact with the sheet to cause the peel charge so that this problem becomes more remarkable.
However, in the above-described conventional magnetic tape cassette, since the travel position of the magnetic tape is regulated by means of the friction sheet, the enhancement in the durability of the friction sheet and the reduction in the surface electric resistance value should be resolved.
Here, the durability of the friction sheet means a cut of the tape edge. The cut of the tape edge may be solved by using a porous sheet as the sheet. Thus, the problem of the durability may be solved.
By the way, in order to reduce the surface electric resistance value of the friction sheet, by utilizing the fact that the sheet is porous, it is possible to consider that, for example, anti-static agent such as a mixture including quaternary ammonium salt is dipped or coated to the sheet so that the anti-static agent is impregnated into the sheet. In the case where the anti-static agent is used for recovering the reduction of the surface electric resistance value of the sheet, the higher the concentration of the anti-static agent, the lower the surface electric resistance value will become, in general.
However, the anti-static agent is impregnated into fine holes formed in the sheet surface, fitted and adhered thereto. For this reason, in some cases, the anti-static agent is peeled off and dropped off by a slight collision. When the concentration of the anti-static agent is increased, not only is the cost increased but also the amount of adhesion of the anti-static agent to the sheet is increased. As a result, the amount of the anti-static agent that drops from the sheet is increased. The drops adhere to the magnetic tape to contaminate the tape and the interior of the cassette. The outer appearance and the product performance are damaged to lead the reduction of the quality of the magnetic tape per se and of the magnetic tape cassette.
Incidentally, a variety of large capacity storage apparatuses are used as storage devices for a computer system. In view of the large capacity of the storage, in particular, a magnetic tape medium is frequently used by a large-scale user. Among these, recently, a cassette type magnetic tape medium, i.e., a magnetic tape cassette is frequently used in view of the fact that it is easy to handle and to provide a large capacity.
As such a magnetic tape cassette, one in which: (take-up) hubs around which the magnetic tape is wound are accommodated on the right and left sides within the case; an opening for drawing out the tape is formed on a front face of the case; the front lid for opening and closing the opening is swingably installed on the front portion of the case; and the a slider that may be slide back and forth is provided on the lower surface side of the case, is used.
On the other hand, a cassette automatic delivery apparatus (hereinafter referred to as an auto loader) is an apparatus for accommodating a plurality of magnetic tape cassettes and delivering the cassettes in order by a delivery mechanism and is connected such that the magnetic tape cassettes are continuously automatically fed to the magnetic head portion of the recording/reproducing apparatus.
As shown in FIG. 12, such an auto loader 140 is structured, for example, as a recirculation type one such that magnetic tape cassettes 81 are inserted into the upper stage of a frame body 142 formed generally into a box shape and are discharged from the lower stage.
In the apparatus exemplified in FIG. 12, seven magnetic tape cassettes 81 as a whole may be accommodated, two magnetic tape cassettes 81 may be loaded on an upper stage guide member 144 formed in rails on the side walls, three magnetic tape cassettes 81 may be overlapped in a deep accommodating portion 146, and furthermore two magnetic tape cassettes 81 may be accommodated in a lower stage delivery portion 148.
The two magnetic tape cassettes 81 inserted onto the upper stage guide member 144 move toward the deep accommodating portion 146, drop by their gravitational force, and overlapped in order as the next magnetic tape cassette 81 is inserted. The lowermost magnetic tape cassette 81 of the deep accommodating portion 146 is delivered from the deep part to the forehand side in the direction indicated by the arrows by a delivery mechanism (not shown) to be moved and discharged in order along the lower stage delivery portion 148.
In the lower stage delivery portion 148, the magnetic tape cassette 81 to be discharged is moved to depress the rear portion of an opposite case 82 to a front lid 91. Incidentally, the details of the delivery mechanism and the opening portion of the frame member 142 through which the delivery mechanism is entered or discharged are not shown in the figures.
In the above-described recirculation type auto loader 140, an upper wall 152 of the upper surface portion of the lower delivery portion 148 is provided with a depression engagement member 150 for positioning and stopping the magnetic tape cassette 81 to be fed out. This depression engagement member 150 is composed of a leaf spring 150b provided with a thin roller 150a on a lower surface side, and one end of the leaf spring 150b is fixed to the above-described upper wall 152 as shown in FIG. 13.
The above-described roller 150a is depressed and contacted with the top surface of the case 82 of the magnetic tape cassette 81 by the biasing force of the leaf spring 150b. Then, a recess 85 is formed on the front side of the top surface of the case 82 in the magnetic tape cassette 81. The roller 150a is engaged with this recess 85 to thereby position the cassette.
Incidentally, since the basic structure of the magnetic tape cassette 81 is the same as that of a magnetic tape cassette 80 shown in FIGS. 6A and 6B to be described later except for a part (structure of the upper wall portion of a front lid 93 and the front end portion of an upper half 83) and the same reference symbols are used to indicate the same or like components, see the explanation thereof. Also, in the following description, the loading direction of the magnetic tape cassette 81 is referred to as the forward direction (direction indicated by the arrow A in FIG. 13) and the direction opposite this is referred to as the backward direction.
However, as described above, in the case where the magnetic tape cassettes 81 are loaded on the recirculation type auto loader 140 having the structure shown in FIG. 12 and delivered in order, when the roller 150a of the depression engagement member 150 for positioning corresponding to the delivery movement is moved under the depression condition on the top surface of the magnetic tape cassette 81, the above-described roller 150a is hooked to the front lid 91 to become an obstacle against the stable delivery movement and to apply an unnecessary (extra) force to the front lid 91 to thereby cause the curvature deformation to depress and open the front lid 91 and to thereby damage it.
Namely, as shown in FIG. 13, when the roller 150a depressed by the biasing force of the leaf spring 150b is engaged with the recess 85 on the upper surface of the case 82 of the magnetic tape cassette 81, the magnetic tape cassette 81 is moved rightward in FIG. 13 (in the direction indicated by the arrow D) by the delivery mechanism, the roller 150a is moved relative to the forward side on the top surface of the case 82 from the recess 85 and enters into a gap 98 defined between the rear end portion of the upper portion of the front lid 91 and the front end portion of the top surface of the case 82 as shown by reference symbol 150a indicated by the broken lines. In some cases, the roller 150a is hooked at the rear end of the top portion of the front lid 91 and elastically deformed such that the central portion of a lid portion 92 is curved forward by means of the delivery force to be subjected to the force of opening (denoted by 92xe2x80x2 indicated by another broken line in FIG. 13). In particular, the central portion of the above-described front lid 91 has a low rigidity and is deformed even by a weak force to expand the gap 98, and the above-described roller 150a is likely to be hooked.
Incidentally, the depression force of the above-described roller 150a is about 1 to 2 N. This is sufficient to depress and position a small size magnetic tape cassette 81. However, the roller 150a is hooked at the front lid 91 as described above and causes the generation of the opening force. If the depression force of the roller 150a is reduced, the generation of the hook at the above-described front lid 91 may be suppressed but there is a problem in that the positioning force is insufficient and unstable.
In view of the above-described problems inherent in the conventional art, a primary object of the present invention is to provide a cassette half and a molding method therefor that may prevent the generation of a weld in a window portion of the cassette half and to prevent the degradation in molding outer appearance in a cassette half whose window portion and upper half body is to be molded in a two-color injection molding.
In view of the above-described problems inherent in the conventional art, a secondary object of the present invention is to provide a magnetic tape cassette that may reduce an amount of wear or cut of a magnetic tape edge per se and a friction sheet while preventing the sticking of the magnetic tape without degrading the anti-static effect to the friction sheet and may remarkably reduce an amount of drop of an anti-static agent due to the friction even if the magnetic tape having the sharp tape edge is used and the friction between the magnetic tape edge and the sheet is kept at a high speed.
In view of the above-described problems inherent in the conventional case, in order to overcome the problems, a third object of the present invention is to provide a magnetic tape cassette in which a detecting roller of an auto loader is prevented from being hooked at a front lid of the magnetic tape cassette so that the front lid is not subjected to the opening force of opening the front lid upon the delivery by the auto loader.
In order to the primary object described above, the first mode of the first aspect of the present invention provides a cassette half molding method for molding one of upper and lower halves with an injection mold by injection molding, the upper and lower halves being coupled with each other in a lid alignment manner to form a cassette case for accommodating a pair of take-up hubs around which a magnetic tape is wound, comprising the step of: molding a transparent or semitransparent window portion provided in the upper half with the injection mold, wherein a gas vent pin for smoothing a flow of molten resin to be introduced in the window portion is provided in the infection mold.
In order to the primary object described above, the second mode of the first aspect of the present invention provides a cassette half that is molded with an injection mold by injection molding and that is one of upper and lower halves that are coupled with each other in a lid alignment manner to form a cassette case for accommodating a pair of take-up hubs around which a magnetic tape is wound, wherein a transparent or semitransparent window portion having a take-up hub position regulating rib is provided on the upper half, and wherein the upper half is molded by the infection mold provided with a gas vent pin for smoothing a flow of molten resin at a portion perpendicular to a flow direction of the molten resin of a ceiling surface of the take-up hub position regulating rib when the window portion is molded by the injection molding.
In order to the secondary object described above, the second aspect of the present invention provides a magnetic tape cassette comprising: a body formed by coupling an upper half and a lower half with each other in a lid alignment manner; a pair of take-up hubs around which a magnetic tape is wound and which are rotatably accommodated in the cassette body; and a friction sheet interposed either between the pair of take-up hubs and the upper half, or between the pair of take-up hubs and the lower half, or both, wherein the thickness of the magnetic tape is equal to or less than 7.7 xcexcm (0.0003 inches), the maximum winding length is equal to or more than 120 m (131.2 yards), and the maximum speed for the tape being wound to the cassette body is 2 m/sec or more, and wherein the friction sheet is made of polyethylene-based resin and has a surface electric resistance value in the range of 1xc3x97107 xcexa9 to 1xc3x971010 xcexa9. 
It is preferable that the polyethylene-based resin is fluorine-based resin in which a part of or all of hydrogen atoms contained in molecules constituting a polymer compound are substituted by fluorine atoms.
In order to the third object described above, the third aspect of the present invention provides a magnetic tape cassette which is loaded onto a cassette auto delivery apparatus for accommodating a plurality of magnetic tape cassettes and for sequentially delivering the magnetic tape cassette by a delivery mechanism, comprising: a body case; a first recess formed in a top surface of the body case for retaining a depression engagement member having a spring and a roller provided in the cassette auto delivery apparatus for positioning and stopping; a front lid provided swingably at a front face of the body case for opening and closing an opening for drawing out a magnetic tape; and a slider disposed in a lower surface of the body case and slidable in backward and forward directions, wherein a rib for reducing a resistance when the roller passes through a gap between the top surface of the body case and the front lid is provided at a position corresponding to the first recess and on a side of the front lid in the top surface of the body case.
It is also preferable that the magnetic tape cassette further comprises a second recess corresponding to a convex portion of the rib at a position of the front lid corresponding to the rib.